1. Field of the Invention
The present invention relates to information recording/reproducing techniques for recording/reproducing information to/from an information recording medium, and more particularly to information recording/reproducing techniques capable of optimizing light radiation power to be used for recording information on the information recording medium, in accordance with the state of the recording medium.
2. Description of the Related Art
Optical disks and the like have already been used practically for recording/reproducing information by using laser beams. One example of rewritable optical disks is a phase change type optical disk which utilizes a reversible phase change between a crystalline state and an amorphous state. In order to obtain the amorphous state, an optical disk is heated to a melting point or higher by applying a high power (record power) and thereafter it is rapidly cooled, and in order to obtain the crystalline state, the optical disk is heated to a crystallization temperature by applying a middle power (erase power) between the high power and a read power and thereafter it is rapidly cooled. By changing the laser power in the above manner, information can be overwritten with a single laser beam. A method of setting an optimum record power when information is written upon radiation of a laser beam, is described in JP-A-7-73466 as a trial write recording control method. With this method, an optimum combination of the record power (high level) and erase power (middle power) for overwrite is decided in the following manner. Information is recorded with a record power having a constant ratio to an erase power, and by lowering the record power, the power level at which an erroneous operation during reproduction starts is detected. By changing the ratio to an erase power, the above operation is repeated. The smallest ratio of the record power to the erase power is obtained, and an operation margin is multiplied by the smallest ratio to determined the optimum record power.
It is a first object of the present invention to provide an information recording/reproducing method, an information recording/reproducing apparatus and an information recording medium capable of high density recording wherein a laser power is changed by detecting reflection light from a recording medium to suppress as much as possible the shape of each record mark from being deformed, to form a high precise record mark and to improve the reliability of data.
It is a second object of the present invention to provide an information recording/reproducing method, an information recording/reproducing apparatus and an information recording medium, capable of increasing a record data transfer speed during high precision overwrite, by switching between preset optimum powers in the record area and in the non-record area.
In order to achieve the first object of the invention, in recording data by changing the state of a record area of a recording medium by applying light, the state of the record area is detected, and in accordance with the detected state, light radiation is controlled.
In this case, the state of the record area is detected from reflection light from the recording medium, and light radiation is controlled in accordance with the n-th (n is a natural number) detected reflection light amount and the (n+1)-th detected reflection light amount. Light radiation is preferably controlled by calculating the (n+1)-th light amount from the n-th light reflection amount and comparing both the amounts.
The above operation is performed periodically or any time as desired. It is therefore possible to suppress as much as possible the shape of each record mark from being deformed, to form a high precise record mark and to improve the reliability of data.
In order to achieve the second object of the invention, prior to recording data, light radiation powers suitable for the states of record and non-record areas are calculated and the calculated radiation powers are selectively used in accordance with the state of each area. In this case, prior to recording data, a record mark and a space are formed in an area excepting the data field of a recording medium, and the light reflection amounts of the record area and non-record area are detected by using the erase power. In accordance with this detection results, at least one of the record and erase powers is preset to control the light radiation.
In this case, as different from the approach to achieve the first object, the preset power levels are switched between the record area and non-record area to perform overwrite. Therefore, it is not necessary to calculate a change ratio of the reflection light amount from the record area to that from the non-record area. Accordingly, the power level can be changed at high speed, the high precision overwrite becomes possible, and the record data transfer rate can be increased.